1. Field of the Invention
This invention relates to thixotropic, water based, general purpose, polyvinyl acetate adhesive gels for wood.
2. Background Art
Many different general purpose adhesives for wood are available. However, such adhesives have various shortcomings such as excessive running when placed on a vertical surface, and difficulty of the dried adhesive: (a) to take a conventional wood stain; (b) to be sanded; or (c) to resist moisture.
This invention provides a thixotropic adhesive gel which can be easily dispensed from a conventional hand held plastic squeeze bottle for wood glue. After being dispensed from the squeeze bottle, the adhesive does not run on vertical surfaces and forms a dry glue line which can be sanded, stained and has resistance to moisture.
The adhesive of this invention comprises and preferably consists essentially of: polyvinyl acetate as the primary adhesive agent; xanthan gum as a thixotropic thickening agent; polyvinyl alcohol as a tackifying agent; and a combination of both wood flour and glyoxal as water resisting agents for the dried adhesive. Additional conventional ingredients used in adhesive compositions such as defoamers, preservatives, and the like can also be use provided that such ingredients or the quantity thereof do not adversely affect the adhesives.
Water based polyvinyl acetate emulsions are popular wood glues. The Handbook of Adhesives, Third Edition which is edited by I. Skeist: pages 388-390 describes the use of polyvinyl alcohol for imparting wet tack and as a protective colloid for polyvinyl acetate emulsions; pages 394-395 discusses thixotropy, pseudoplasticity and thickening of polyvinyl acetate with various materials; and page 398 describes the use of foam control agents and biocides in such adhesives.
U.S. Pat. No. 3,442,845 of May 6, 1969 to P. Columbus et al. relates to polyvinyl acetate adhesives which, upon drying, are redispersible in cold or hot water. The adhesive compositions of the 845 patent use polyvinyl alcohol, water-soluble gums, and cellulose ethers as anti-coalescing agents for the polyvinyl acetate. Propylene glycol and other polyhydroxy compounds are mentioned as plasticizers for polyvinyl alcohol.
U.S. Pat. No. 4,251,400 of Feb. 17, 1981 to P. Columbus also relates to a polyvinyl acetate adhesive which is redispersible in hot and cold water in the dried film form and which uses polyvinylpyrrolidone and a non-volatile, water-soluble, plasticizer as the anti-coalescing agent. In addition to the polyvinyl acetate and polyvinylpyrrolidone that patent also mentions the use of polyvinyl alcohol, propylene glycol, as well as water-soluble ethers in the adhesive composition.
European Patent Application Publication Number 0210052 to Locktite which was published on Jan. 28, 1987 relates to various tubes for dispensing reactive adhesives such as cyanoacrylate at a rate of one or two drops at a time. The patent mentions resilient plastic tube dispensers and broadly states that the adhesive can be thixotropic.
Technical Bulletin DB-15 entitled "KELZAN, Xanthan Gum", of Merck & Co. describes xanthan gum as a thickener and suspending agent for water based systems and promotes its suspending, pseudoplastic (thixotropic), and stability properties.
KELCO XANTHAN GUM, Third Edition, of Kelco a division of Merck & Co. shows much the same as the above KELZAN bulletin, and also states that its xanthan gum provides smooth flow under sheer in adhesive formulations and that this allows the application of high solids.
U.S. Pat. No. 3,676,174 Uses a mixture of wood flour and plaster of Paris to form a paintable base for molded articles. In Col. 2, step 5, it discloses a composition of: I part plaster of Paris; 1 part of wood flour; and 6 parts fine metal powder. This dry powder is mixed with an equal quantity of polyvinyl acetate solution diluted with water and is used as a coating on clay objects.
U.S. Pat. No. 2,510,257 Discloses an aqueous polyvinyl acetate emulsion adhesive containing glyoxal and polyvinyl alcohol. The glyoxal imparts water resistance to the adhesive.
U.S. Pat. No. 4,638,022 Uses polyvinyl acetate together with pecan shell flour to provide a coating for wood or plastic which accepts conventional wood stains. The composition of this reference appears to be in an organic solvent system.
A commercial product called "Glue Gap 202 GF Filling" of the Garott Wade Company, Inc. which is located at 161 Sixth Avenue, New York, N.Y. is an aqueous polyvinyl acetate emulsion adhesive which contains wood fibers or wood flour. This product is viscous but has little or no thixotropy; also, much of the wood fiber appears to settle easily and requires shaking to disperse the wood fibers.